Adjustable resistance device



Jan. 12, 1960 E. R. LUTHER ,2 3

ADJUSTABLE RESISTANCE DEVICE Filed Oct. 29, 1958 2 Sheets-Sheet 1 'F' .4. R .9. ii fi y 1N VENTOR Eouwvo R05 5R7 L UTHER ATTORNEYS Jan. 12, 1960 E. R. LUTHER ADJUSTABLE RESISTANCE DEVICE 2 Sheets-Sheet 2 Filed Oct. 29, 1958 United States Patent 2,921,283 ADJUSTABLE RESISTANCE DEVICE Edmund R. Luther, Fort Worth, Tex., assignor to B & H

Instrument Company, Inc., Fort Worth, Tex., a corporation of Texas Application October 29, 1958, Serial No. 770,405 6 Claims. (Cl. 338-79) adjustable resistance demember, has electrical resistance properties, and the member from point to point therealong carries indicia positioned on the member at locations corresponding to electrically determined resistance values. Hitherto unrealized accuracy is obtained because changes in resistance along the member or element do not accumulate. The copending application. Serial No. 716,350, R. L. Hartung, filed February 20, 1958 (original filed November 7, 1957),, assigned to the present assignee, describes an embodiment wherein the indicia along the member are physical manifestations engageable by a cooperating member. The illustrative case there given has the indicia on the member as apertures, engaged by teeth of a sprocket wheel.

The present invention constitutes an improvement in compactly handling the elongated member as it is moved relative to the contact region whereat the indicia are sensed and electrical contact made with the resistive member or element. Briefly stated, means for reeling the elongated indicia and resistancecarrying member is provided' for reeling the elongated member or element about a common axis. In an illustrated form one end of the elongated member is on one spool and the other end. on another spool. having a coincident axis. Transfer means are provided, rotatable about said axis, for picking up themember from one spool and setting it down on the other, and vice-versa. as relative rotation is reversed. Contact means engages the member in its passage between the spools. The illustrated form of the invention provides sprocket means between the spools for engaging the indicia, illustrated by apertures in the member, for positioning or locating the member with certainty with respect to the contact. means for reading by the latter.

Accordingly, a primary object of the present invention is to provide an improved adjustableresistance device of the type wherein indicia are positionedalong a memher in terms of actual electrically measured resistance values.

A further object of the invention is to provide a compact adjustable impedance device wherein rotary position of'amember is continuously related to impedance values without accumulation of errors.

Further objects and the entire scope of the invention will become further apparent from the following detailed description of an illustrative embodiment of the invention. This embodiment can be most readily understood with reference to the accompanying drawings,

wherein:

'Figure 1 shows a side elevational view of an embodimentof the invention with the cover partially in crosstwflsa.-. I

Figure 2 shows a cross-section of a typical elongated indicia carrying and resistance member used in the invention, and a contact member used therewith.

Figure 3 shows a cross-section of another form of elongated indicia carrying and resistance member.

Figure 4 shows a somewhat enlarged cross-sectional side elevational view of the device shown in Figure 1.

Figure 5 is a diagrammatic illustration of certain principal parts of the device of Figures 1 and 4.

Figure 6 is an end cross-sectional view taken along the line 6-6 of Figure 1.

Figure 7 is an end cross-sectional view taken along the line 77 of Figure 1.,

Figure 8 is an. end cross-sectional view taken along the line 88 of Figure 1.

Figure 9 is an end cross-sectional view taken along the line 99 of Figure 1.

Figure 10 is an inside end elevational view of a cage structure which forms a part of the device of Figures 1-4 and 9.

Figure 11 is a side elevational view of the structure of Figure 10, with a movable panel extended outwardly from its position in Figure 10, and

Figure 12 is a view similar to Figure 10, but with the movable panel extended outwardly as shown in Figure 11.

In the illustrated embodiment reference character 10 (Fig. 1) designates the elongated member at least a lengthwise portion of which is electrically conductive and has desiredresistance properties. Member 10 may be of insulating material with a resistance element 12 attached to one edge,'as shown in Figure 2. Or member 10 may be a combination of a layer 10 having the resistance properties and a layer 14 of insulating material provided as in Figure 3 to avoid shortcircuiting when coiled as on a reel or spool. In the Figure 2 case, the diameter of 12 can be less than the thickness of 10 to preclude shorting when reeled up. The main feature in any case is that the member 10 having integral or attached resistive properties be capable of carrying indicia from point to point along its length. Copending application Serial No. 572,758 describes several suitable designs of such elongated members.

In the above mentioned copending applications it is explained that a contact means engages the resistive aspect or portion of member 10 between the ends thereof, so that adjustable resistance be available from said contact and one or both ends of the member 10. The applications further explain that indicia are placed from point to point along the member at positions determined by an actual electrical determination of resistance. The final aspect of the invention is that a location means is provided in predetermined positional relation to the contact means, to insure that when indicia are sensed, the member 10 presents the corresponding point of resistance value to the contact means, or vice versa.

In Williams Serial No. 572,758 various embodiments show indicia printed upon member 10 (or 14) and sensed by the eye through a locator means in the form of a window. In Hartung Serial No. 716,350 the indicia are in engageable form such as apertures in the elongated member, the positions or other characteristics of which may vary to accommodate variations in the resistive properties of the elongated member. In Serial No. 716,350 the locator means is a member which can engage the indicia so as to cause the rotational position of a shaft, for example, to be directly related to previously measured resistance values at the point of contact of the contact means.

The above mentioned applications show the indicia carrying member reeled between two spools or reels which revolve about spaced apart parallel axes. By the present invention, a far more compact package is provided by reeling the member to either side of the contact-locator means about a common or coincident axis.

'As can be most easily observed initially from Figures '1- and 4 the structured the illustrated embodiment of the present invention comprises a body or frame 16 characterized by a circular disc part 18 and an elongated cylindrical part 20. Body 16 and other partsare preferably made of an insulating material, as suggested by the insulation-type cross-hatching in the drawings. Parts 18 and 20 of body 16 are further characterized by a cylindrical aperture 22 extending centrally thereof throughout the length of the part 20. Into aperture 22 is-fitted as by press-fit a hollow stem or bushing member 24 freely rotatable within which is a shaft 26 extending through bushing 24- and terminating at shaft end 26' at the left-hand side of Figure 4. A typical retaining snap ring 28 may be provided at the point whereshaft 26 enters the bushing 24 at the right-hand side as shown in Figures 1 and 4. At the other end of the shaft a pin 30 (Fig. 4) may be provided for securing the shaft 26 to a cage-like structure comprising a circular end plate 32 and a contact carrying arm 34 and guide or transfer arms 36 (Fig. 4) and 38 (Fig. 1). As best seen in Figure 8 the contact carrying arm 34 has aifixed thereto contact 40 and to either side thereof extensions 34a and 3412.

Returning to Figure 4, the cylindrical part of body 16 carries a first circular disc 42 and a second circular disc 44. 'Ihusly, disc 42 together with the inner surface of disc 32 and the intervening portion of part 20 forms a spool or reel on which the elongated member can be reeled up. Figure 7 is a cross-sectional view within the just described spool or reel and shows member 10 having two convolutions therein. Member 10 may terminate in a flexible metal anchor piece 10' aflixed to member 10 along a length thereof and finally anchored to the part the end of-cylindrical part reels defined by discs in part by disc 42 (see Fig. 7). ber of convolutions of the member 10 on this spool and dictable flexing and therefore variable length of member 10 between the particular indicia and its resistance point. Thusly, the extremely high order to accuracy explained in the above mentioned copending applications is achieved.

The contact member may be of resilient bronze or the like, and at its end may be provided with a small piece oflsilver or good contact metal 40 .(Fig. 2). Contact member 40 may becarried in a dhannel along the outer surface-of contact arm 34 and then brought wardly to a yoke 4011 (Figs. 4, 9 and'S) for slidablyand electrically engaging a slip ring 64 fixedly embedded in 20' of body 16. Slip'ring 64 may be connected by electrical conductor 66 embedded in parts 20 and 18 of body 16 for providing terminal 68.

The guide arms 36 and 38 serve to lift or transfer the elongated member 10 out of the respective spools or for permitting a length of member 10 to pass the locator and contact areas and then re-enter the other spool or reel. Starting from anchor point 46 in the spool defined There may be any nummember 10 then'leads outwardly and over the guide arm 36. After passing over guide arm 36, the member 10, as new best seen in Figure 8, proceeds to be engaged by thesprocket teeth 60 in the vicinity of contact member 40. For insuring engagement of the sprocket teeth 60 20 of body 16 as at 46 wherefrom an electrical lead 48 (Fig. 5) embedded in part 20 may connect to a terminal post 50. 1

Similarly, disc 44 together with the inner surface 18 of part 18 of body 16 and the intervening section of part 20 of body 16, forms a second spool or reel on which the member 10 maybe reeled up. I Figure 6 is a view within this reel or spool chamber, showing a part of member 10, with an anchor piece 10' as described above, and anchored as at point 52 wherefrom an electrical lead 54- (Fig. 5) embedded in part 20 may connect with a terminal 56.

' From Figure 8 it can be most readily observed that the guide arms 36 and 38 are-preferably about 120 apart, and the contact carrying arm 34 about 120 from each of theaforesaid guide arms.

Between discs 42 and 44 there is provided a means for locating the indicia on the member 10 so as to provide Ia correlated resistance reading by the contact member 40 which engages the resistive portion of the member 10. In the illustrated embodiment the locator means is a sprocket wheel 58 having teeth 60 which engage variously placed indicia apertures 62 existing in the'member 10 in accordance with the above mentioned copending application of Hartung, Serial No. 716,350. Briefly stated, the teeth 60 of the sprocket 58 must be equally a particular rotational position with respect to body 16,

the contact 40 will be at a precise rotational position with respect to the sprocket 58. The resistance values along the member 10 are opposite or reasonably closeto the related engageable indicia, so therecan be no 111 1 7? post 7 0,

with the aperture 62 of member 10, contact arm 34 is provided with an inwardly extending post 70 (Fig. 4)

having an extreme end surface 70a which bears upon 'the member 10 beside the teeth 60 so as to insure seating of the member" 10 on the sprocket, and with a recessed section 70b for just clearing the extremities of the sprocket teeth 60., Returning to Figure 8, after leaving the locator position adjacent contact 40 and contact arm the member 10 is trained over the guide arm 38 wherefrom it enters the spool or reel defined in part by disc 44. The entry of member 10 into the just mentioned .spool is shown in Figure 6. See also Figure 1 for the member 10 overlying the guide arm 38 for transferring the'member 10 into the right-hand spool.

The thickness of guide arm 38 may be reduced to the 'right ofpoint 38 in Figure 1 so as to provide ample clearance between the outer surface of the right-hand "end of guide arm 38 and a cylindrical cover 72 having a closed end 74 which may be slipped over the assembly and fixed by any suitable means such as pin 76 (Fig. 4) to the part 18 of body 16. The thickness of guide arm 36 in the vicinity of the spool defined by disc 42 may :be similarly of lesser thickness than the portion thereover overlying the spool defined by disc 44, as shown at point 36' in Figure 11.

The extension of guide arm 36 to encompass the spool defined by disc 44, and the part of guide arm 38 which encompasses a part of the .spool defined by disc 42, together with the previously mentioned extensions 34a and 34b of the contact arm 34 serve to restrain the member 10 within the respective spools. The cover 72 also serves this purpose. It is to be understood that the member 10 even if of paper or like insulating material,

when having a resistance element such as -12 (Fig. 2)

fixed along one edgefhas considerable resiliency. Also, theconvolutions of element 10 on the respective spools cannot be wound too tightly, but should have enough slack so that changing overall diameters due to changing numbers of convolutions in the respective spools will not cause a tightening against either one of the anchor points 46 and 52. Accordingly, there will be somev tendency of the convolutions of the element 10 to spring outwardly and the restraint as, provided bythe aforesaid guide arms 36 and 38 and the extensions 34a-and34b are useful.

A feature of the present invention concerns' 'the'ar- 42 and 44, etc., as above described mgementr forr assemblin'gs'the various parts, 'WhiDhJWill;

now be described with particular: regard to Figures 110;. l1 and 12 in addition to the other figures.

Inasmuch as the contact 40 and the post 70 of contact arm 34 extend inwardly of the, outer peripheries of disc 44, there must be some way'of assembling the parts. This isdone in accordance with. the invention by providing the" disc 32 with a. sliding partition: 32a which carries the contact arm 34 together with contact 40, post 70 and yoke 40a. Tongues 32b may be cut into the edges of disc 32 (Fig. 12) which cooperate with the grooves 320 (Fig. ll) in the edges of the panel 32a to maintain the panel 32a on the disc 32. Figure shows the panel 32a pushed inwardly to be in its final position, while Figures 11 and 12 show the panel 32a together with the contact arm 34 and other parts, slidably extending outwardly from the central shaft 26.

The structure may be assembled by first taking the body 16 and anchoring the respective ends of the element 10 to the anchor points 46 and 52. The cage-like structure made up of disc 32, guide arms 36 and 38 and the shaft 26 may then be positioned over the body, with the panel 32a removed. This is done by sliding the shaft 26 through bushing 24 with ring 28 removed. The element 10 should be trained over the arms 36 and 38 as described hereinabove to leave the length of element 10 available for engagement by the sprocket between the arms 36 and 38 as best shown in Figure 8. Now the panel 32a may be slidably inserted on the disc 32 and the post 70 and contact 40 will then descend between the discs 42 and 44. During this stage of the assembly a particular one of the sprocket teeth, which can be previously marked if desired, should be inserted into a predetermined one of the apertures 62 of the element 10, so as to positively correlate the rotational position of the shaft 26 with a known value of resistance from one end or the other of the element 10.

The device is operated by imparting relative move ment between the shaft 26 and the body 16. Considering the several views in Figures 1, 8, 7 and 6, if the shaft 26 as viewed in Figure 8 together with the guide arms 36 and 38 and the contact arm 34 are rotated counterclockwise with respect to the body 16 and sprocket 58, the guide arm 38 will lift the element 10 out of the right-hand spool (as viewed in Fig. 1), permit same to engage the sprocket wheel by walking around the sprocket, and after the element 10 passes over the guide arm 36 it will be disposed in convolutions in the left-hand spool. Opposite relative rotation between shaft 26 and body 16 will result in the transfer of the element 10 back across the sprocket into the other spool. Depending upon the size of the device in relation to the thickness of the element 10, a great number of convolutions of member 10 and therefore many rotations of the shaft 26 with respect to the body 16 may be accomplished.

It will be understood that resistance reading is in terms of the relative rotational positions of the shaft 26 and body 16, and, accordingly, rotational position of a shaft in terms of resistance is provided just as in the above mentioned Hartung application. This rotational resistance reading is extremely precise, for the reasons given in both of the above mentioned applications. The particular advantage is that small errors in resistivity of the elongated member are not permitted to accumulate, due to the position of the indicia in terms of actual electrical measured values of resistance, and the fact that the position of the resistive portion of the element cannot alter itself in relation to the position of the related indicia.

It will be understood that the body 16 may be secured to a fixed structure such as an instrument panel, and the shaft '26 connected to some piece of rotating equipment in which the potentiometer is used. Of course, the reverse is true, that the shaft 26 and/or structure fixed thereto can be secured and the body 16 rotated.

The foregoing: detailed. description is. given onlyihl, purposes of illustration, and: the; scope'of the invention is: to be determined from the appendedv claims.

What is, claimed is:

1. An adjustable resistance device having a two-ended elongated member at least a portion. of which has, resistiveproperties, engageable, indicia on; the. member posi tioned thereon with respect; to electrically determ ned resistance values of said resistive portion, means for reeling said member about a common given axis, contact means rotatable about said axis for movably engaging the resistive portion of said member between the ends thereof, and means for continuously engaging said indicia at a predetermined position relative to said contact means for locating the contacting point of said contact means on said elongated member with respect to particular indicia.

2. An adjustable resistance device comprising means forming a first spool having a hub and side walls, means mounting said spool for rotation about an axis, a second such spool mounted to the side of said first spool for rotation about said axis, an elongated member having one end on said first spool and its other end on said second spool, at least a lengthwise portion of the member having resistance properties and engageable indicia placed along the electrical member in accordance with related electrically measured resistance values, transfer means movable in rotation about said axis relative to said spools, the just mentioned means including guide means overlying said spools, the guide means having openings therein adjacent each spool, the elongated member between its ends threading outwardly from one spool through an opening in said guide means and threading inwardly through another opening of said guide means to said second spool, contact means mounted for movement with the guide means for contacting the resistive portion of the elongated member at a point thereof as it passes between said spools, and means engageable with said indicia for locating the contact point of said contact means on said elongated member with respect to particular indicia, the arrangement being such that relative rotation between said indicia engaging means and said guide means transfers the elongated member from one spool to the other.

3. A device as in claim 2 wherein the indicia engaging means has equally spaced means thereon for engaging the indicia on said elongated member for continuously positioning said elongated member relative to said contact means as the elongated member is passed between the spools, and means for moving said indicia engaging member about said axis relative to said guide means.

4. A device as in claim 3 wherein the indicia on the elongated member are apertures placed therealong in accordance with electrically determined values of resistance of the member, and the means engaging said apertures is a sprocket having equally spaced teeth about its circumference.

5. An adjustable resistance device comprising a body structure having an end disc portion and a cylindrical part, further discs parallel to the end disc and spaced along said cylindrical part, a sprocket on said cylindrical part intermediate said further discs, cage structure rotatable about said cylindrical part, the cage structure comprising an end disc and spaced apart guide and contact arms extending over said further disc and sprocket of said cylindrical part, the contact arm having an inwardly extending post terminating in proximity to the sprocket, an apertured elongated member having one end anchored on said cylindrical part in a reel area between the end disc of the cylindrical part and one further disc to reel up therebetween, the other end of the elongated member anchored to the cylindrical part in a reel area between the other further disc of the cylindrical part and the end disc of the cage structure to reel up therebetween, the elongated member between its ends trained over. said guide 8 meat of the cage structure relative to the body stmc ture' for assembly or disassembly.

"References Cited in the file ofthis :pateut; l

iJNrTE STATES PAT NTS Bliss Apr. 1 a, 1936 Wi1liams Nov. 11, 1958 

